1. Field of the Invention
The invention relates to a microphone array in a housing receiving sound via guide tubes.
2. Description of the Related Art
A microphone array includes a number of microphones disposed in tandem. A simple example is shown in FIG. 1, wherein the microphone array 10 includes two microphones 11 and 12 placed side by side. Directivity of the microphone array 10 can be achieved by manipulating the signal received by the two microphones 11 and 12. Assuming the two microphones 11 and 12 are omni-directional and having the same characteristics, the directivity of the microphone array 10 depends on vector {right arrow over (d)} from one microphone 11 to the other microphone 12.
The above-mentioned microphones 11 and 12 are conventionally placed in an open space to achieve directivity. Most electronic devices (cellular phones, personal digital assistants, etc.), however, have plastic or metal housings, acting as acoustic isolators which block audio signals, thus increasing the difficulty of microphone placement. Furthermore, the majority of electronic elements including microphones are conventionally surface-mounted on printed circuit boards (PCBs), thus limiting the directivity of the microphone array. As illustrated by FIG. 2, microphones 11′ and 12′ are disposed in a housing 20. The housing 20 acts as an acoustic isolator preventing the microphones 11′ and 12′ from receiving external sound. Furthermore, the distance d1 between the microphones 11′ and 12′ on the PCB 21 is limited by the available space on the PCB 21 and in the housing 20, generally being less than the desired distance (d1<d). Furthermore, the direction of the microphone array, as designated by vector {right arrow over (d1)}, is always parallel to the PCB 21. Such a direction, however, does not necessarily target the desired sound source during operation of the electronic device.